Christopher Posted January 30, 2005 Report Share Posted January 30, 2005 Click here for bios on each of the four major developers.— What is the history of ATRAC development?Suzuki: ATRAC made its debut in 1992 with the launch of the MiniDisc. In 1999, as a new feature of the MiniDisc called MDLP, we introduced ATRAC3, which delivered an improved compression ratio. And just as electronic music distribution started becoming popular, we introduced ATRAC3plus in 2002.— Is the technology behind these codecs very different?Suzuki: The basic technology is much the same. All codecs take as their input a PCM sound source. They perform signal processing on a fixed number of samples which are converted into frequency data and then compressed (encoded). At the other end, these steps are performed in reverse, so the data is decoded. After restoring the frequency data, signal processing reproduces the PCM sound source. With each codec, there's a difference in the number of samples used for frequency conversion: the higher the compression ratio, the larger the number of samples.— In developing the codec, what was the most important thing for you?Suzuki: The balance between audio quality and hardware resources.Inoue: The ATRAC algorithm is implemented in hardware, an LSI, so the goal of our development is a tangible product. To achieve this, it's necessary for the LSI team and the algorithm team to coordinate their development work. That's one of the major differences between ATRAC and other codecs – not many other codecs have been developed in tandem with hardware.Tsuji: It's a huge burden on the LSI if you try to make it process each and every single task that comes along. So it's important for the algorithm and LSI development teams to find the point at which there is a practical trade-off. For example, when developing ATRAC3plus, the algorithm that I was in charge of threatened to be a severe headache for the LSI team, but after several meetings we worked it out.Inoue: Yes, our premise that hardware should efficiently process ATRAC encoding is especially important for us. In many cases, the encoding for other codecs is based only on software processing on a PC. But an essential feature of the MiniDisc, for example, is recording from the hardware unit. That's why, when we developed the specifications for ATRAC, we had to make sure the LSI could process the encoding at high speeds and with minimal power consumption.— What was behind the development of ATRAC3plus?Inoue: We developed ATRAC3plus at a time when it seemed we had to answer a variety of demands – including both low bit rates and high bit rates.Toyama: The ATRAC3 specification was originally developed to achieve a sound quality equivalent to the MiniDisc at 132kbps, so there was a limit to what kind of quality we could expect at a lower bit rate. But we applied technologies to solve the various obstacles we had faced in the past and focussed on crafting a new sound that would satisfy changing demands. ATRAC3plus is the result. In subjective evaluation tests conducted by third parties in 2003, it was confirmed that ATRAC3plus at 64kbps offers sound quality equivalent to MP3 at 128kbps.Inoue: The demand for low bit rates started to coincide with the capacity increase of hard disk drives and other storage media, which meant, for some people, that a high compression ratio was not the most important criterion, as long as they could record with high quality.Suzuki: Yes. Users who put more emphasis on sound quality than on the number of tracks.Inoue: The answer for them is ATRAC3plus at 256kbps. CDs are 1,411kbps, so we are talking about 1/5 the size, but audio quality is almost as good as the original CD.Toyama: In recent subjective evaluation tests, we proved that it's almost impossible to tell the difference in sound quality between ATRAC3plus at 256kbps and CDs at 1,411kbps.The process of encoding anddecoding is repeated ad infinitum. — You were talking about crafting the sound, but how do you go about optimizing or tuning?Suzuki: Sound is subjective. Something about a particular sound may really grab your attention, yet someone else won't even notice it. When that happens, you get friends of like mind together and make that someone feel bad! (laughter)Toyama: For example, people who play instruments tend to pay attention to the sound of each instrument, but your average person enjoys music as an overall experience. Everyone listens to music differently, so it's dangerous for just one person to do the tuning. I've played a variety of instruments, so when I listen to music I pay attention to how they sound, and the quality of vocals as well.Suzuki: I'm the opposite. I listen to the whole thing. I belong to the generation that grew up with Walkman – music accompanies my activities. I don't notice the parts, but take in the whole song. As you can see, even within our team, we listen to music differently. But we don't give priority to one type of listening. It's important to find the best balance – that's our approach. So whenever I make progress in crafting sound, I get Tsuji and Inoue to join me in the listening room for several hours to get their opinions.Listening room: here theATRAC sound is carefully crafted.— What exactly is involved in this process of tuning?Suzuki: We repeatedly encode and decode. In other words, we process the signal, compress it, reconstitute it and then listen to it again. Usually we use headphones, but when doing an overall check we pipe it through speakers in the listening room.— Is there a difference between listening on headphones and listening through speakers?Suzuki: Oh, completely different. To check details of the sound, headphones are the thing. But speakers are essential when you want to check the ambiance, harmonious sound, balance, and so on. You may think you've achieved a really beautiful sound, only to find that in an open listening space, that's not the case.Tsuji: And because our constant tweaking is affected by our surroundings, we can't work in an open-plan layout to do our tuning. Our workspace isn't very large, but it's divided up with high partitions.Suzuki: When tuning, we use a database of sound sources created especially for evaluation. For example, Mariah Carey is extremely tricky because the instruments and the vocals range over a very wide spectrum. And we can't make an encoder by just targeting a particular band. I've been listening to Mariah for 8 years – tens of thousands of times. Now I don't need to listen to the original sound source: just listening to the decoded sound I can tell whether it's good or not. I think her songs are indelibly impressed on my memory.Testing equipment: providesessential support for thecodec developers.— And I understand that the results of this tuning are then evaluated by Sony Music (SME)?Suzuki: Our work with SME started when they wanted to know whether or not they could use our codec for distributing music electronically. We asked them to assess our encoder and found them to be incredibly tough critics! (laughter)Toyama: SME distributes music electronically and whatever codec they use, they're responsible for delivering the end result to paying customers. Obviously it's no good if the sound quality doesn't satisfy SME. That's why we've worked hard to tune the codec to win SME's approval.— The codec used in SME's online music distribution is ATRAC3?Suzuki: That's right. The sound we created around 2000 is still being distributed today. But there were times when the development team and SME didn't agree. Developers tend to emphasize details, but SME values an overall balanced sound. We use sound sources they give us for tuning, after which recording staff at the SME studio test the codec rigorously for things like sound localization and coherence.Toyama: The sound sources from SME are their own special mix. They know it front to back, exactly what sounds are where. So if something is even slightly off, they know immediately.Suzuki: Because you're compressing sound, it can't be helped if the result doesn't sound the same as the original. But it's not acceptable if the compressed sound changes the impression of the original, so balance is especially important.Toyama: That's right. We look closely at how the compressed result sounds. Even with compression, people want the music to sound good, if not great.Suzuki: To be precise, while admitting ATRAC3 compressed sound is not the same as the original, we've arrived at the point where the way in which the sound has changed, is good – good enough for the ears of the recording staff at SME.— What about ATRAC3plus?Tsuji: SME has yet to evaluate ATRAC3plus. Originally we targeted our development for compact media such as flash memory. So we focused on high compression ratios and worked hard to craft good sound quality, even for bit rates as low as 48kbps and 64kbps.Suzuki: If the bit rate is high enough, there's enough data to cover any shortcoming even if the encoder doesn't work exactly as hoped. But the lower the bit rate, the more likely it will be affected should the encoder performance be just a little wanting – it would appear as noise or otherwise sound poor. That's why we spent a lot of time enhancing the 48kbps and 64kbps encoders. We're confident that they sound better than any competing codec. In the future, with the cooperation of SME, we want to make audio quality even better. — Recently, the rising popularity of personal audio players equipped with hard disks has increased the interest in codecs. As codec developers what would you like to see in ATRAC3plus-compliant products?Inoue: For our part, we will continue to work hard on codec development, and we'd like product developers to continue to focus on crafting the quality of the sound at the point where it is converted from digital to analogue.Suzuki: Of course, product developers are concerned with the whole player, but I think it's an advantage for audio manufacturers like us if we can optimize each of the components that make up a player. As a user myself, that's what I expect.— As ATRAC developers, do you have a message for the readers?Tsuji: Some people seem to have the bias that "compressed sound is bad", which I think is a bit of a shame. Maybe it just comes from familiarity with linear PCM compact discs – their very presence helps create this impression of inferiority. I really hope that people put aside any prejudice they may have and listen to compressed music with an open mind.Toyama: I once worked in an SME mastering studio for a month as part of my production training, and was surprised to find the vast number of sounds in a CD recording. If you compare compressed music to that, of course it isn't the same, but it does create new ways to enjoy music, such as online music, and lets you store a lot more songs on recording media. Whether we're talking about a natural shift in sound quality, or being able to enjoy music for hours without getting tired, what we do, we do for music – after all, we love music. And we'll keep on developing to expand the possibilities of sound.Suzuki: When we created the ATRAC3plus algorithm we put a lot of emphasis on high quality sound. So I would ask the readers to experience it first-hand, and at different bit rates.Inoue: Yes, our ultimate goal as developers is to have listeners appreciate just how good the music sounds without noticing the bit rates. We will continue to work hard to craft the kind of sounds that allow people to enjoy music naturally and with the greatest pleasure. Quote Link to comment Share on other sites More sharing options...
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